Skin Adipocyte Stem Cell Self-Renewal Is Regulated by a PDGFA/AKT-Signaling Axis

Dermal white adipose tissue: Development and impact on hair follicles, skin defense, and fibrosis

Dermal white adipose tissue (DWAT) is a distinctive adipose depot located within the lower dermis of the skin. Its significance as an ancillary fat in skin homoeostasis has recently received increased attention. New research has revealed that DWAT responses to skin pathology and physiology changes, impacting skin development, hair cycling, defense mechanisms, and fibrotic conditions. In this review, we explore the developmental process of DWAT and the adipose commitment timing of hypodermal. We explore the development process of DWAT and its pivotal role in regulating the hair cycle. We conclude the antibacterial activity and reversible dedifferentiation of dermal adipocytes in response to skin defense. Furthermore, we underscore the potentially crucial yet underestimated anti-fibrotic functions of DWAT-derived adipokines and adipocyte-myofibroblast transition.

Biliary fibrosis is an important but neglected pathological feature in hepatobiliary disorders: from molecular mechanisms to clinical implications

Fibrosis resulting from pathological repair secondary to recurrent or persistent tissue damage often leads to organ failure and mortality. Biliary fibrosis is a crucial but easily neglected pathological feature in hepatobiliary disorders, which may promote the development and progression of benign and malignant biliary diseases through pathological healing mechanisms secondary to biliary tract injuries. Elucidating the etiology and pathogenesis of biliary fibrosis is beneficial to the prevention and treatment of biliary diseases. In this review, we emphasized the importance of biliary fibrosis in cholangiopathies and summarized the clinical manifestations, epidemiology, and aberrant cellular composition involving the biliary ductules, cholangiocytes, immune system, fibroblasts, and the microbiome. We also focused on pivotal signaling pathways and offered insights into ongoing clinical trials and proposing a strategic approach for managing biliary fibrosis-related cholangiopathies. This review will offer a comprehensive perspective on biliary fibrosis and provide an important reference for future mechanism research and innovative therapy to prevent or reverse fibrosis.

Therapeutic targeting of white adipose tissue metabolic dysfunction in obesity: mechanisms and opportunities

White adipose tissue is not only a highly heterogeneous organ containing various cells, such as adipocytes, adipose stem and progenitor cells, and immune cells, but also an endocrine organ that is highly important for regulating metabolic and immune homeostasis. In individuals with obesity, dynamic cellular changes in adipose tissue result in phenotypic switching and adipose tissue dysfunction, including pathological expansion, WAT fibrosis, immune cell infiltration, endoplasmic reticulum stress, and ectopic lipid accumulation, ultimately leading to chronic low-grade inflammation and insulin resistance. Recently, many distinct subpopulations of adipose tissue have been identified, providing new insights into the potential mechanisms of adipose dysfunction in individuals with obesity. Therefore, targeting white adipose tissue as a therapeutic agent for treating obesity and obesity-related metabolic diseases is of great scientific interest. Here, we provide an overview of white adipose tissue remodeling in individuals with obesity including cellular changes and discuss the underlying regulatory mechanisms of white adipose tissue metabolic dysfunction. Currently, various studies have uncovered promising targets and strategies for obesity treatment. We also outline the potential therapeutic signaling pathways of targeting adipose tissue and summarize existing therapeutic strategies for antiobesity treatment including pharmacological approaches, lifestyle interventions, and novel therapies.

[Research progress in regulation of hair growth by dermal adipose tissue]

Objective

To summarize the dynamic and synchronized changes between the hair cycle and dermal adipose tissue as well as the impact of dermal adipose tissue on hair growth, and to provide a new research idea for the clinical treatment of hair loss.

Methods

An extensive review of relevant literature both domestic and international was conducted, analyzing and summarizing the impact of dermal adipose precursor cells, mature dermal adipocytes, and the processes of adipogenesis in dermal adipose tissue on the transition of hair cycle phases.

Results

Dermal adipose tissue is anatomically adjacent to hair follicles and closely related to the changes in the hair cycle. The proliferation and differentiation of dermal adipose precursor cells promote the transition of hair cycle from telogen to anagen, while mature adipocytes can accelerate the transition from anagen to catagen of the hair cycle by expressing signaling molecules, with adipogenesis in dermal adipose tissue and hair cycle transition signaling coexistence.

Conclusion

Dermal adipose tissue affects the transition of the hair cycle and regulates hair growth by secreting various signaling molecules. However, the quantity and depth of existing literature are far from sufficient to fully elucidate its prominent role in regulating the hair cycle, and the specific regulatory mechanisms needs to be further studied.

Involvement of DKK1 secreted from adipose-derived stem cells in alopecia areata

Adipose-derived stem cells (ASCs) have shown efficacy in promoting hair growth, while DKK1 inhibits the WNT pathway, which is associated with hair loss. Our study focused on investigating the expression of DKK1 in alopecia areata (AA), a condition characterised by significant increases in the DKK1 levels in human and mouse ASCs. Treatment of interferon-γ increased the expression of DKK1 via STAT3 phosphorylation in ASCs. Treatment with recombinant DKK1 resulted in a decrease of cell growth in outer root sheath cells, whereas the use of a DKK1 neutralising antibody promoted hair growth. These results indicate that ASCs secrete DKK1, playing a crucial role in the progression and development of AA. Consequently, we generated DKK1 knockout (KO) ASCs using the Crispr/Cas9 system and evaluated their hair growth-promoting effects in an AA model. The DKK1 KO in ASCs led to enhanced cell motility and reduced cellular senescence by activating the WNT signalling pathway, while it reduced the expression of inflammatory cytokines by inactivating the NF-kB pathway. As expected, the intravenous injection of DKK1-KO-ASCs in AA mice, and the treatment with a conditioned medium derived from DKK1-KO-ASCs in hair organ culture proved to be more effective compared with the use of naïve ASCs and their conditioned medium. Overall, these findings suggest that DKK1 represents a novel therapeutic target for treating AA, and cell therapy using DKK1-KO-ASCs demonstrates greater efficiency.

Local and systemic mechanisms that control the hair follicle stem cell niche

Hair follicles are essential appendages of the mammalian skin, as hair performs vital functions of protection, thermoregulation and sensation. Hair follicles harbour exceptional regenerative abilities as they contain multiple somatic stem cell populations such as hair follicle stem cells (HFSCs) and melanocyte stem cells. Surrounding the stem cells and their progeny, diverse groups of cells and extracellular matrix proteins are organized to form a microenvironment (called 'niche') that serves to promote and maintain the optimal functioning of these stem cell populations. Recent studies have shed light on the intricate nature of the HFSC niche and its crucial role in regulating hair follicle regeneration. In this Review, we describe how the niche serves as a signalling hub, communicating, deciphering and integrating both local signals within the skin and systemic inputs from the body and environment to modulate HFSC activity. We delve into the recent advancements in identifying the cellular and molecular nature of the niche, providing a holistic perspective on its essential functions in hair follicle morphogenesis, regeneration and ageing.

Tumor-mesothelium HOXA11-PDGF BB/TGF β1-miR-181a-5p-Egr1 feedforward amplifier circuity propels mesothelial fibrosis and peritoneal metastasis of gastric cancer

A proportion of gastric cancer (GC) patients suffer from peritoneal metastasis (PM) in the late stage of tumor and these patients have a poor prognosis. To provide more care for GC patient with PM, a deeper exploration of the molecular characteristics of GC-PM is needed. Here we performed the in vitro and in vivo study to illustrate the effect of HOXA11 over-expressed GC cells on peritoneal mesothelial cells (HMrSV5), transcriptomics analyses of HMrSV5 cells co-cultured with HOXA11 over-expressed GC cells, counterparts or alone, cytokine array analyses of serum-free culture medium of HOXA11 over-expressed GC cells, we validated our findings through genetic manipulation of HMrSV5 cells and neutralizing antibodies targeting cytokines secreted by HOXA11 over-expressed GC cells in vitro, as well as utilized human peritoneal metastatic lesions to validate expression of potential targets. We identified that HOXA11 over-expressed GC cells strongly propelled mesothelial fibrosis in vivo and in vitro, and HOXA11 regulated paracrine and autocrine of PDGF BB and TGF β1 in GC cells to propel mesothelial fibrosis. Meanwhile, HOXA11 over-expressed GC cells drove PDGF BB and TGF β1 secretion to activate developmental-process related genes in HMrSV5 cells, including Egr1, which processes dependent on miR-181a-5p. Then, Egr1 could mediate peritoneal mesothelial fibrosis. Correspondingly, Egr1 over-expressed HMrSV5 cells supported migration and peritoneal dissemination of GC cells. Together our results suggest that a feedforward amplifier circuity governing GC cells and mesothelial cells in peritoneum contribute to peritoneal metastasis of GC cells.

Fibroblasts in immune-mediated inflammatory diseases: The soil of inflammation

As one of the most abundant stromal cells, fibroblasts are primarily responsible for the production and remodeling of the extracellular matrix. Traditionally, fibroblasts have been viewed as quiescent cells. However, recent advances in multi-omics technologies have demonstrated that fibroblasts exhibit remarkable functional diversity at the single-cell level. Additionally, fibroblasts are heterogeneous in their origins, tissue locations, and transitions with stromal cells. The dynamic nature of fibroblasts is further underscored by the fact that disease stages can impact their heterogeneity and behavior, particularly in immune-mediated inflammatory diseases such as psoriasis, inflammatory bowel diseases, and rheumatoid arthritis, etc. Fibroblasts can actively contribute to the disease initiation, progression, and relapse by responding to local microenvironmental signals, secreting downstream inflammatory factors, and interacting with immune cells during the pathological process. Here we focus on the development, plasticity, and heterogeneity of fibroblasts in inflammation, emphasizing the need for a developmental and dynamic perspective on fibroblasts.

Regulation of adipocyte dedifferentiation at the skin wound edge

Adipocytes have diverse roles in energy storage and metabolism, inflammation, and tissue repair. Mature adipocytes have been assumed to be terminally differentiated cells. However, recent evidence suggests that adipocytes retain substantial phenotypic plasticity, with potential to dedifferentiate into fibroblast-like cells under physiological and pathological conditions. Here, we develop a two-step lineage tracing approach based on the observation that fibroblasts express platelet-derived growth factor receptor alpha ( Pdgfra ) while adipocytes express Adiponectin ( Adipoq ) but not Pdgfra . Our approach specifically traces Pdgfra + cells that originate from Adipoq + adipocytes. We find many traced adipocytes and fibroblast-like cells surrounding skin wounds, but only a few traced cells localize to the wound center. In agreement with adipocyte plasticity, traced adipocytes incorporate EdU, downregulate Plin1 and PPARγ, and upregulate αSMA. We also investigate the role of potential dedifferentiation signals using constitutively active PDGFRα mutation, Pdgfra knockout, or Tgfbr2 knockout models. We find that PDGF and TGFβ signaling both promote dedifferentiation, and PDGFRα does so independently of TGFβR2. These results demonstrate an intersectional genetic approach to trace the hybrid cell phenotype of Pdgfra + adipocytes, which may be important for wound repair, regeneration and fibrosis.

TET3 plays a critical role in white adipose development and diet-induced remodeling

Maintaining healthy adipose tissue is crucial for metabolic health, requiring a deeper understanding of adipocyte development and response to high-calorie diets. This study highlights the importance of TET3 during white adipose tissue (WAT) development and expansion. Selective depletion of Tet3 in adipose precursor cells (APCs) reduces adipogenesis, protects against diet-induced adipose expansion, and enhances whole-body metabolism. Transcriptomic analysis of wild-type and Tet3 knockout (KO) APCs unveiled TET3 target genes, including Pparg and several genes linked to the extracellular matrix, pivotal for adipogenesis and remodeling. DNA methylation profiling and functional studies underscore the importance of DNA demethylation in gene regulation. Remarkably, targeted DNA demethylation at the Pparg promoter restored its transcription. In conclusion, TET3 significantly governs adipogenesis and diet-induced adipose expansion by regulating key target genes in APCs.

Feasibility of adipose-derived therapies for hair regeneration: Insights based on signaling interplay and clinical overview

Dermal white adipose tissue (dWAT) is a dynamic component of the skin and closely interacts with the hair follicle. Interestingly, dWAT envelops the hair follicle during anagen and undergoes fluctuations in volume throughout the hair cycle. dWAT-derived extracellular vesicles can significantly regulate the hair cycle, and this provides a theoretical basis for utilizing adipose tissue as a feasible clinical strategy to treat hair loss. However, the amount and depth of the available literature are far from enough to fully elucidate the prominent role of dWAT in modulating the hair growth cycle. This review starts by investigating the hair cycle-coupled dWAT remodeling and the reciprocal signaling interplay underneath. Then, it summarizes the current literature and assesses the advantages and limitations of clinical research utilizing adipose-derived therapies for hair regeneration.

Mature white adipocyte plasticity during mammary gland remodelling and cancer

Mammary gland growth and differentiation predominantly rely on stromal-epithelial cellular communication. Specifically, mammary adipocytes play a crucial role in ductal morphogenesis, as well as in the proliferation and differentiation of mammary epithelial cells. The process of lactation entails a reduction in the levels of white adipose tissue associated with the MG, allowing for the expansion of milk-producing epithelial cells. Subsequently, during involution and the regression of the milk-producing unit, adipocyte layers resurface, occupying the vacated space. This dynamic phenomenon underscores the remarkable plasticity and expansion of adipose tissue. Traditionally considered terminally differentiated, adipocytes have recently been found to exhibit plasticity in certain contexts. Unraveling the significance of this cell type within the MG could pave the way for novel approaches to reduce the risk of breast cancer and enhance lactation performance. Moreover, a comprehensive understanding of adipocyte trans- and de-differentiation processes holds promise for the development of innovative therapeutic interventions targeting cancer, fibrosis, obesity, type 2 diabetes, and other related diseases. Additionally, adipocytes may find utility in the realm of regenerative medicine. This review article provides a comprehensive examination of recent advancements in our understanding of MG remodelling, with a specific focus on the tissue-specific functions of adipocytes and their role in the development of cancer. By synthesizing current knowledge in this field, it aims to consolidate our understanding of adipocyte biology within the context of mammary gland biology, thereby fostering further research and discovery in this vital area.

Platelet-derived growth factor PDGF-AA upregulates connexin 43 expression and promotes gap junction formations in osteoblast cells through p-Akt signaling

Gap junctions, which are mainly composed of connexin units, play an indispensable role in cell morphogenesis, proliferation, migration, adhesion and differentiation of osteoblast lineage cells, and thus mediate bone development, homeostasis and disease occurrence. Platelet-derived growth factor-AA (PDGF-AA) is proved to have a great influence on osteoblast cell lines and is widely applied in the field of bone defect and wound healing. However, the role of PDGF-AA on gap junction formation in the osteoblast lineage remains elusive. In the current study, we aimed to investigate the impact of PDGF-AA on gap junction formation and cell-to-cell communication in the osteoblast lineage and explore its underlying biomechanism. We first found that PDGF-AA promoted cell proliferation and thus increased gap junction formations in living primary osteoblasts and MC3T3-E1 cells through scrape loading and dye transfer (SL/DT) assay. We then confirmed that PDGF-AA enhanced gap junction formations through up-regulation of connexin 43 (Cx43). We next detected the activation of p-Akt signaling in primary osteoblasts and MC3T3-E1 cells that were induced by PDGF-AA. Through inhibitory experiments, we further confirmed that PDGF-AA-mediated gap junction formation occurred via the activation of PI3K/Akt signaling. Taking together, our results provided evidences that PDGF-AA promoted gap junction formation in the osteoblast lineage through p-Akt signaling, which helped to understand the role of PDGF-AA in bone regeneration and diseases.

Dynamic interplay between IL-1 and WNT pathways in regulating dermal adipocyte lineage cells during skin development and wound regeneration

Dermal adipocyte lineage cells are highly plastic and can undergo reversible differentiation and dedifferentiation in response to various stimuli. Using single-cell RNA sequencing of developing or wounded mouse skin, we classify dermal fibroblasts (dFBs) into distinct non-adipogenic and adipogenic cell states. Cell differentiation trajectory analyses identify IL-1-NF-κB and WNT-β-catenin as top signaling pathways that positively and negatively associate with adipogenesis, respectively. Upon wounding, activation of adipocyte progenitors and wound-induced adipogenesis are mediated in part by neutrophils through the IL-1R-NF-κB-CREB signaling axis. In contrast, WNT activation, by WNT ligand and/or ablation of Gsk3, inhibits the adipogenic potential of dFBs but promotes lipolysis and dedifferentiation of mature adipocytes, contributing to myofibroblast formation. Finally, sustained WNT activation and inhibition of adipogenesis is seen in human keloids. These data reveal molecular mechanisms underlying the plasticity of dermal adipocyte lineage cells, defining potential therapeutic targets for defective wound healing and scar formation.

Single-cell lineage tracing reveals hierarchy and mechanism of adipocyte precursor maturation

White adipose tissue is crucial in various physiological processes. In response to high caloric intake, adipose tissue may expand by generating new adipocytes. Adipocyte precursor cells (progenitors and preadipocytes) are essential for generating mature adipocytes, and single-cell RNA sequencing provides new means to identify these populations. Here, we characterized adipocyte precursor populations in the skin, an adipose depot with rapid and robust generation of mature adipocytes. We identified a new population of immature preadipocytes, revealed a biased differentiation potential of progenitor cells, and identified Sox9 as a critical factor in driving progenitors toward adipose commitment, the first known mechanism of progenitor differentiation. These findings shed light on the specific dynamics and molecular mechanisms underlying rapid adipogenesis in the skin.

A Wrong Fate Decision in Adipose Stem Cells upon Obesity

Progress has been made in identifying stem cell aging as a pathological manifestation of a variety of diseases, including obesity. Adipose stem cells (ASCs) play a core role in adipocyte turnover, which maintains tissue homeostasis. Given aberrant lineage determination as a feature of stem cell aging, failure in adipogenesis is a culprit of adipose hypertrophy, resulting in adiposopathy and related complications. In this review, we elucidate how ASC fails in entering adipogenic lineage, with a specific focus on extracellular signaling pathways, epigenetic drift, metabolic reprogramming, and mechanical stretch. Nonetheless, such detrimental alternations can be reversed by guiding ASCs towards adipogenesis. Considering the pathological role of ASC aging in obesity, targeting adipogenesis as an anti-obesity treatment will be a key area of future research, and a strategy to rejuvenate tissue stem cell will be capable of alleviating metabolic syndrome.

Postprandial triglyceride-rich lipoproteins promote the adipogenic differentiation of adipose-derived mesenchymal stem cells via the LRP1/caveolin-1/AKT1 pathway

Diet-induced obesity (OB) is usually accompanied by hypertriglyceridemia, which is characterized by the accumulation of triglyceride (TG)-rich lipoprotein (TRL) particles in the circulation. We previously found that postprandial TRL combined with insulin induced the adipogenic differentiation of 3T3-L1 preadipocytes, which may represent a key mechanism underlying obesity. However, the specific mechanism and signaling pathway involved in this process remain to be fully elucidated. In this study, we found that, in the postprandial state, patients with obesity had significantly higher levels of TG and remnant cholesterol (RC) than normal-weight controls. In vitro, we found that postprandial TRL, together with insulin, promoted the adipogenic differentiation of adipose-derived mesenchymal stem cells (AMSCs), as evidenced by the increased expression of lipogenesis-related genes and their protein products, including low-density lipoprotein related protein 1 (LRP1). Besides, caveolin-1 (Cav-1) expression was also significantly upregulated under this condition. Cav-1 and LRP1 were observed to interact, and then led to the activation of the PI3K/AKT1 signaling pathway. Meanwhile, the inhibition of LRP1 or Cav-1 significantly attenuated the adipogenic differentiation of AMSCs and downregulated AKT1 phosphorylation levels. Moreover, treatment with a selective AKT1 inhibitor significantly suppressed postprandial TRL and insulin-induced adipogenesis in AMSCs. Combined, our results demonstrated that, in association with insulin, postprandial TRL can promote the adipogenic differentiation of AMSCs in a manner that is dependent on the LRP1/Cav-1-mediated activation of the PI3K/AKT1 signaling pathway. Our findings indicated that a postprandial increase in TRL content is a critical factor in the pathogenesis of hypertriglyceridemia and diet-induced obesity.

Genome characterization of Hirame novirhabdovirus (HIRRV) isolate CNPo2015 and transcriptome analysis of Hirame natural embryo (HINAE) cells infected with CNPo2015

Hirame novirhabdovirus (HIRRV) is a fish rhabdovirus belonging to family Rhabdoviridae, genus Novirhabdovirus, which is highly contagious and virulent, and causes hemorrhagic disease in many fish species. In the present work, the whole genome sequence of HIRRV strain CNPo2015 that previously isolated from cultured flounders was obtained using high-throughput sequencing. It consists of 10,998 nucleotides and encodes six viral proteins arranged in order of 3'-N-P-M-G-NV-L-5'. Among Novirhabdovirus, L protein of CNPo2015 possessed the lowest amino acid sequence divergence with HIRRV isolate CA 9703 and HIRRV 080113, and the highest with Snakehead rhabdovirus. Furthermore, the immune response of Hirame natural embryo (HINAE) cell line to HIRRV infection was characterized by RNA-seq, and the results showed that 1976 differentially expressed genes (DEGs) including 1219 up-regulated and 727 down-regulated genes were identified in the HINAE cells infected with HIRRV at 48 h post infection (hpi). Several KEGG pathways were significantly enriched in the viral infected cells, such as cytokine-cytokine receptor interaction, JAK-STAT signaling pathway, cell cycle, apoptosis, RIG-I-like receptors signaling pathway and P13K-AKT signaling pathway. Post viral infection, the flow cytometric Annexin V/PI assay found that apoptotic rate of HINAE cells showed a slight increase within 3 days and then the early and late apoptotic rate were significantly increased to 41 ± 2.65% and 12.37 ± 2.61% at day 4, respectively. Meanwhile, qRT-PCR results also showed that six apoptosis-related genes (BCL2L1, CASPASE 3, CASPASE 10, FAS, AKT and CDK1) were significantly upregulated. This investigation has not only enriched our knowledge of sequence difference characteristics between CNPo2015 and other Novirhabdoviruses, but also provided a data basis for deeper understanding of immune responses in flounder cells post viral infection.

Adipose tissue-derived small extracellular vesicles modulate macrophages to improve the homing of adipocyte precursors and endothelial cells in adipose tissue regeneration

Rapid infiltration of endogenous cells induced by cell-free biomaterials is the first and crucial step in tissue regeneration and macrophage is largely involved. Our previous study reported adipose tissue-derived small extracellular vesicles (sEV-AT) could successfully promote adipose tissue regeneration. However, the role of macrophages in this process was unknown. In this study, we isolated sEV-AT and subcutaneously implanted it into the back of SD rats. The results showed sEV-AT increased macrophage infiltration significantly, which was followed by improving homing of adipocyte precursors (APs) and endothelial cells (ECs). However, when macrophages were depleted by clodronate liposome within 1 week, the homing of APs and ECs, and adipose tissue regeneration were destroyed. In vitro, sEV-AT showed the ability to promote the migration of macrophages directly. Besides, sEV-AT-pretreated macrophages improved the migration of APs and ECs, accompanied by the increase of chemokines (MCP-1, SDF-1, VEGF, and FGF) and the activation of NF-kB signaling pathway. These findings indicated sEV-AT might regulate the secretion of chemokines via activating NF-kB signaling pathway to improve homing of APs and ECs and facilitate adipose tissue regeneration. These findings deepened our understanding of small extracellular vesicle-induced tissue regeneration and laid a theoretical foundation for the clinical application of sEV-AT.

Identification of Candidate Genes and Regulatory Competitive Endogenous RNA (ceRNA) Networks Underlying Intramuscular Fat Content in Yorkshire Pigs with Extreme Fat Deposition Phenotypes

Intramuscular fat (IMF) content is vital for pork quality, serving an important role in economic performance in pig industry. Non-coding RNAs, with mRNAs, are involved in IMF deposition; however, their functions and regulatory mechanisms in porcine IMF remain elusive. This study assessed the whole transcriptome expression profiles of the Longissimus dorsi muscle of pigs with high (H) and low (L) IMF content to identify genes implicated in porcine IMF adipogenesis and their regulatory functions. Hundreds of differentially expressed RNAs were found to be involved in fatty acid metabolic processes, lipid metabolism, and fat cell differentiation. Furthermore, combing co-differential expression analyses, we constructed competing endogenous RNAs (ceRNA) regulatory networks, showing crosstalk among 30 lncRNAs and 61 mRNAs through 20 miRNAs, five circRNAs and 11 mRNAs through four miRNAs, and potential IMF deposition-related ceRNA subnetworks. Functional lncRNAs and circRNAs (such as MSTRG.12440.1, ENSSSCT00000066779, novel_circ_011355, novel_circ_011355) were found to act as ceRNAs of important lipid metabolism-related mRNAs (LEP, IP6K1, FFAR4, CEBPA, etc.) by sponging functional miRNAs (such as ssc-miR-196a, ssc-miR-200b, ssc-miR10391, miR486-y). These findings provide potential regulators and molecular regulatory networks that can be utilized for research on IMF traits in pigs, which would aid in marker-assisted selection to improve pork quality.

Novel prospects for scarless wound healing: The roles of myofibroblasts and adipocytes

Disturbances or defects in the process of wound repair can disrupt the delicate balance of cells and molecules necessary for complete wound healing, thus leading to chronic wounds or fibrotic scars. Myofibroblasts are one of the most important cells involved in fibrotic scars, and reprogramming provides a potential avenue to increase myofibroblast clearance. Although myofibroblasts have long been recognized as terminally differentiated cells, recent studies have shown that myofibroblasts have the capacity to be reprogrammed into adipocytes. This review intends to summarize the potential of reprogramming myofibroblasts into adipocytes. We will discuss myofibroblast lineage tracing, as well as the known mechanisms underlying adipocyte regeneration from myofibroblasts. In addition, we investigated different changes in myofibroblast gene expression, transcriptional regulators, signalling pathways and epigenetic regulators during skin wound healing. In the future, myofibroblast reprogramming in wound healing will be better understood and appreciated, which may provide new ideas for the treatment of scarless wound healing.

Modulating Cellular Responses to Mechanical Forces to Promote Wound Regeneration

Significance: Skin scarring poses a major biomedical burden for hundreds of millions of patients annually. However, this burden could be mitigated by therapies that promote wound regeneration, with full recovery of skin's normal adnexa, matrix ultrastructure, and mechanical strength. Recent Advances: The observation of wound regeneration in several mouse models suggests a retained capacity for postnatal mammalian skin to regenerate under the right conditions. Mechanical forces are a major contributor to skin fibrosis and a prime target for devices and therapeutics that could promote skin regeneration. Critical Issues: Wound-induced hair neogenesis, Acomys "spiny" mice, Murphy Roths Large mice, and mice treated with mechanotransduction inhibitors all show various degrees of wound regeneration. Comparison of regenerating wounds in these models against scarring wounds reveals differences in extracellular matrix interactions and in mechanosensitive activation of key signaling pathways, including Wnt, Sonic hedgehog, focal adhesion kinase, and Yes-associated protein. The advent of single-cell "omics" technologies has deepened this understanding and revealed that regeneration may recapitulate development in certain contexts, although it is unknown whether these mechanisms are relevant to healing in tight-skinned animals such as humans. Future Directions: While early findings in mice are promising, comparison across model systems is needed to resolve conflicting mechanisms and to identify conserved master regulators of skin regeneration. There also remains a dire need for studies on mechanomodulation of wounds in large, tight-skinned animals, such as red Duroc pigs, which better approximate human wound healing.

Adipocyte plasticity in tissue regeneration, repair, and disease

Mammalian tissue repair forms a scar that fills the injured area with a fibrotic lesion, limiting tissue function. Adipocytes, lipid-filled cells, well-known for energy storage and endocrine functions, can reside adjacent to or within many tissues, and are emerging as critical regulators of tissue repair. In this review, the plasticity and function of adipocytes to tissue repair and fibrosis in four tissues: skin, heart, skeletal muscle, and mammary gland, will be discussed. The dynamic nature of adipocytes as they release bioactive products, lipids, and adipokines, and their ability to form contractile fibroblasts, is emerging as an essential regulator of wound healing and tumorigenesis in multiple tissues. Thus, modulation of adipocytes may provide therapeutic avenues for regenerative medicine and cancer.

Temporal control of PDGFRα regulates the fibroblast-to-myofibroblast transition in wound healing

Fibroblasts differentiate into myofibroblasts by acquiring new contractile function. This is important for tissue repair, but it also contributes to organ fibrosis. Platelet-derived growth factor (PDGF) promotes tissue repair and fibrosis, but the relationship between PDGF and myofibroblasts is unclear. Using mice with lineage tracing linked to PDGF receptor α (PDGFRα) gene mutations, we examine cell fates during skin wound healing. Elevated PDGFRα signaling increases proliferation but unexpectedly delays the fibroblast-to-myofibroblast transition, suggesting that PDGFRα must be downregulated for myofibroblast differentiation. In contrast, deletion of PDGFRα decreases proliferation and myofibroblast differentiation by reducing serum response factor (SRF) nuclear localization. Consequences of SRF deletion resemble PDGFRα deletion, but deletion of two SRF coactivators, MRTFA and MRTFB, specifically eliminates myofibroblasts. Our findings suggest a scenario where PDGFRα signaling initially supports proliferation of fibroblast progenitors to expand their number during early wound healing but, later, PDGFRα downregulation facilitates fibroblast differentiation into myofibroblasts.

Building and Maintaining the Skin

The skin forms a crucial, dynamic barrier between an animal and the external world. In mammals, three stem cell populations possess robust regenerative potential to maintain and repair the body's protective surface: epidermal stem cells, which maintain the stratified epidermis; hair follicle stem cells, which power the cyclic growth of the hair follicle; and melanocyte stem cells, which regenerate pigment-producing melanocytes to color the skin and hair. These stem cells reside in complex microenvironments ("niches") comprising diverse cellular repertoires that enable stem cells to rejuvenate tissues during homeostasis and regenerate them upon injury. Beyond their niches, skin stem cells can also sense and respond to fluctuations in organismal health or changes outside the body. Here, we review these diverse cellular interactions and highlight how far-reaching signals can be transmitted at the local level to enable skin stem cells to tailor their actions to suit the particular occasion and optimize fitness.

Daidzein Activates Akt Pathway to Promote the Proliferation of Female Germline Stem Cells through Upregulating Clec11a

Female germline stem cells (FGSCs) have been successfully isolated and characterized from postnatal mammalian and human ovarian tissues. However, the effects and mechanisms of action of natural small-molecule compounds on FGSCs are largely unknown. Here, we found that daidzein promoted the viability and proliferation of FGSCs. To elucidate the mechanism underlying this, we performed RNA-Sequence in daidzein-treated FGSCs and controls. The results showed that there were 153 upregulated and 156 downregulated genes in daidzein treatment. We confirmed the expression of some genes related to cell proliferation in the sequencing results by RT-PCR, such as Type C lectin domain family 11 member a (Clec11a), Mucin1 (Muc1), Glutathione peroxidase 3 (Gpx3), and Tet methylcytosine dioxygenase 1 (Tet1). The high expression of Clec11a at the protein level after daidzein treatment was also confirmed by western blotting. Furthermore, recombinant mouse Clec11a (rmClec11a) protein was shown to promote the viability and proliferation of FGSCs. However, knockdown of Clec11a inhibited the viability and proliferation of FGSCs, which could not be rescued by the administration of daidzein. These results indicate that daidzein promoted the viability and proliferation of FGSCs through Clec11a. In addition, both daidzein and rmClec11a activated the Akt signaling pathway in FGSCs. However, Clec11a knockdown inhibited this pathway, which could not be rescued by daidzein administration. Taken together, our findings revealed that daidzein activates the Akt signaling pathway to promote cell viability and proliferation through upregulating Clec11a. This study should deepen our understanding of the developmental mechanism of FGSCs and female infertility.

Skin Fibrosis and Recovery Is Dependent on Wnt Activation via DPP4

Fibrosis is the life-threatening, excessive accumulation of the extracellular matrix and is sometimes associated with a loss of lipid-filled cells in the skin and other organs. Understanding the mechanisms of fibrosis and associated lipodystrophy and their reversal may reveal new targets for therapeutic intervention. In vivo genetic models are needed to identify key targets that induce recovery from established fibrosis. Wnt signaling is activated in animal and human fibrotic diseases across organs. Here, we developed a genetically inducible and reversible Wnt activation model and showed that it is sufficient to cause fibrotic dermal remodeling, including extracellular matrix expansion and shrinking of dermal adipocytes. Upon withdrawal from Wnt activation, Wnt-induced fibrotic remodeling was reversed in mouse skin-fully restoring skin architecture. Next, we demonstrated CD26/ DPP4 is a Wnt/β-catenin-responsive gene and a functional mediator of fibrotic transformation. We provide genetic evidence that the Wnt/DPP4 axis is required to drive fibrotic dermal remodeling and is associated with human skin fibrosis severity. Remarkably, DPP4 inhibitors can be repurposed to accelerate recovery from established Wnt-induced fibrosis. Collectively, this study identifies Wnt/DPP4 axis as a key driver of extracellular matrix homeostasis and dermal fat loss, providing therapeutic avenues to manipulate the onset and reversal of tissue fibrosis.

Mechanical tension mobilizes Lgr6+ epidermal stem cells to drive skin growth

Uniquely among mammalian organs, skin is capable of marked size change in adults, yet the mechanisms underlying this notable capacity are unclear. Here, we use a system of controlled tissue expansion in mice to uncover cellular and molecular determinants of skin growth. Through machine learning-guided three-dimensional tissue reconstruction, we capture morphometric changes in growing skin. We find that most growth is driven by the proliferation of the epidermis in response to mechanical tension, with more limited changes in dermal and subdermal compartments. Epidermal growth is achieved through preferential activation and differentiation of Lgr6⁺ stem cells of the epidermis, driven in part by the Hippo pathway. By single-cell RNA sequencing, we uncover further changes in mechanosensitive and metabolic pathways underlying growth control in the skin. These studies point to therapeutic strategies to enhance skin growth and establish a platform for understanding organ size dynamics in adult mammals.

Fibroblasts Mediate Ectopic Bone Formation of Calcium Phosphate Ceramics

Heterogeneity of fibroblasts directly affects the outcome of tissue regeneration; however, whether bioactive ceramics regulate bone regeneration through fibroblasts is unclear. Ectopic bone formation model with biphasic calcium phosphate (BCP) implantation was used to investigate the temporal and spatial distribution of fibroblasts around ceramics. The effect of BCP on L929 fibroblasts was evaluated by EdU assay, transwell assay, and qRT-PCR. Further, the effect of its conditioned medium on osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) was confirmed by ALP staining. SEM and XRD results showed that BCP contained abundant micro- and macro-pores and consisted of hydrogen-apatite (HA) and β-tricalcium phosphate (β-TCP) phases. Subsequently, BCP implanted into mice muscle successfully induced osteoblasts and bone formation. Fibroblasts labelled by vimentin gathered around BCP at 7 days and peaked at 14 days post implantation. In vitro, BCP inhibited proliferation of L929 fibroblast but promoted its migration. Moreover, expression of Col1a1, Bmp2, and Igf1 in L929 treated by BCP increased significantly while expression of Tgfb1 and Acta did not change. ALP staining further showed conditioned media from L929 fibroblasts treated by BCP could enhance osteogenic differentiation of BMSCs. In conclusion, fibroblasts mediate ectopic bone formation of calcium phosphate ceramics.

Platelet‐Derived Growth Factor Receptor Type α Activation Drives Pulmonary Vascular Remodeling Via Progenitor Cell Proliferation and Induces Pulmonary Hypertension

Background

Platelet‐derived growth factor is a major regulator of the vascular remodeling associated with pulmonary arterial hypertension. We previously showed that protein widely 1 (PW1⁺) vascular progenitor cells participate in early vessel neomuscularization during experimental pulmonary hypertension (PH) and we addressed the role of the platelet‐derived growth factor receptor type α (PDGFRα) pathway in progenitor cell‐dependent vascular remodeling and in PH development.

Methods and Results

Remodeled pulmonary arteries from patients with idiopathic pulmonary arterial hypertension showed an increased number of perivascular and vascular PW1⁺ cells expressing PDGFRα. PW1^nLacZ reporter mice were used to follow the fate of pulmonary PW1⁺ progenitor cells in a model of chronic hypoxia–induced PH development. Under chronic hypoxia, PDGFRα inhibition prevented the increase in PW1⁺ progenitor cell proliferation and differentiation into vascular smooth muscle cells and reduced pulmonary vessel neomuscularization, but did not prevent an increased right ventricular systolic pressure or the development of right ventricular hypertrophy. Conversely, constitutive PDGFRα activation led to neomuscularization via PW1⁺ progenitor cell differentiation into new smooth muscle cells and to PH development in male mice without fibrosis. In vitro, PW1⁺ progenitor cell proliferation, but not differentiation, was dependent on PDGFRα activity.

Conclusions

These results demonstrate a major role of PDGFRα signaling in progenitor cell–dependent lung vessel neomuscularization and vascular remodeling contributing to PH development, including in idiopathic pulmonary arterial hypertension patients. Our findings suggest that PDGFRα blockers may offer a therapeutic add‐on strategy to combine with current pulmonary arterial hypertension treatments to reduce vascular remodeling. Furthermore, our study highlights constitutive PDGFRα activation as a novel experimental PH model.

Remodeling of dermal adipose tissue alleviates cutaneous toxicity induced by anti-EGFR therapy

Anti-epidermal growth factor receptor (EGFR) therapy–associated cutaneous toxicity is a syndrome characterized by papulopustular rash, local inflammation, folliculitis, and microbial infection, resulting in a decrease in quality of life and dose interruption. However, no effective clinical intervention is available for this adverse effect. Here, we report the atrophy of dermal white adipose tissue (dWAT), a highly plastic adipose tissue with various skin-specific functions, correlates with rash occurrence and exacerbation in a murine model of EGFR inhibitor-induced rash. The reduction in dWAT is due to the inhibition of adipogenic differentiation by defects in peroxisome proliferator-activated receptor γ (PPARγ) signaling, and increased lipolysis by the induced expression of the lipolytic cytokine IL6. The activation of PPARγ by rosiglitazone maintains adipogenic differentiation and represses the transcription of IL6, eventually improving skin functions and ameliorating the severity of rash without altering the antitumor effects. Thus, activation of PPARγ represents a promising approach to ameliorate cutaneous toxicity in patients with cancer who receive anti-EGFR therapy.

Young fibroblast-derived exosomal microRNA-125b transfers beneficial effects on aged cutaneous wound healing

Aged skin wounds heal poorly, resulting in medical, economic, and social burdens posed by nonhealing wounds. Age-related defects in repair are associated with reduced myofibroblasts and dysfunctional extracellular matrix (ECM) deposition. Bidirectional cell-cell communication involving exosome-borne cargo such as micro RNAs (miRs) has emerged as a critical mechanism for wound healing and aged tissue regeneration. Here we report that at the wound edge, aged fibroblasts display reduced migration and differentiation into myofibroblasts, with impaired ECM deposition, when compared with young tissue. Proper activation of fibroblasts to myofibroblasts may alleviate age-related defects in wound healing. Herein, an exosome-guided cell technique was performed to induce effective wound healing. Supplementing wounds with exosomes isolated from young mouse wound-edge fibroblasts (exosomes^Young) significantly improved the abundance of myofibroblasts and wound healing in aged mice and caused fibroblasts to migrate and transition to myofibroblasts in vitro. To determine the underlying mechanism, we found that exosomal transfer of miR-125b to fibroblasts inhibited sirtuin 7 (Sirt7), thus accelerating myofibroblast differentiation and wound healing in aged mice. Notably, after epidermal inhibition of miR-125b or overexpression of Sirt7 in fibroblasts, migration and myofibroblast transition were perturbed. Our findings thus reveal that miR-125b is transferred through exosomes from young fibroblasts to old fibroblasts contributes to promoting fibroblast migration and transition to counteract aging, suggesting a potential avenue for anti-aging interventions in wound healing.

Contrasting recruitment of skin-associated adipose depots during cold challenge of mouse and human

KEY POINTS

Several distinct strategies produce and conserve heat to maintain the body temperature of mammals, each associated with unique physiologies, with consequences for wellness and disease susceptibility Highly regulated properties of skin offset the total requirement for heat production  We hypothesize that the adipose component of skin is primarily responsible for modulating heat flux; here we evaluate the relative regulation of adipose depots in mouse and human, to test their recruitment to heat production and conservation We found that insulating mouse dermal white adipose tissue accumulates in response to environmentally and genetically induced cool stress; this layer is one of two adipose depots closely apposed to mouse skin, where the subcutaneous mammary gland fat pads are actively recruited to heat production In contrast, the body-wide adipose depot associated with human skin produces heat directly, potentially creating an alternative to the centrally regulated brown adipose tissue ABSTRACT: Mammalian skin impacts metabolic efficiency system-wide, controlling the rate of heat loss and consequent heat production. Here we compare the unique fat depots associated with mouse and human skin, to determine whether they have corresponding functions and regulation. For humans, we assay a skin-associated fat (SAF) body-wide depot to distinguish it from the subcutaneous fat pads characteristic of the abdomen and upper limbs. We show that the thickness of SAF is not related to general adiposity; it is much thicker (1.6-fold) in women than men, and highly subject-specific. We used molecular and cellular assays of β-adrenergic-induced lipolysis and found that dermal white adipose tissue (dWAT) in mice is resistant to lipolysis; in contrast, the body-wide human SAF depot becomes lipolytic, generating heat in response to β-adrenergic stimulation. In mice challenged to make more heat to maintain body temperature (either environmentally or genetically), there is a compensatory increase in thickness of dWAT: a corresponding β-adrenergic stimulation of human skin adipose (in vivo or in explant) depletes adipocyte lipid content. We summarize the regulation of skin-associated adipocytes by age, sex and adiposity, for both species. We conclude that the body-wide dWAT depot of mice shows unique regulation that enables it to be deployed for heat preservation; combined with the actively lipolytic subcutaneous mammary fat pads they enable thermal defence. The adipose tissue that covers human subjects produces heat directly, providing an alternative to the brown adipose tissues.

Thymic macrophages consist of two populations with distinct localization and origin

Tissue-resident macrophages are essential to protect from pathogen invasion and maintain organ homeostasis. The ability of thymic macrophages to engulf apoptotic thymocytes is well appreciated, but little is known about their ontogeny, maintenance, and diversity. Here, we characterized the surface phenotype and transcriptional profile of these cells and defined their expression signature. Thymic macrophages were most closely related to spleen red pulp macrophages and Kupffer cells and shared the expression of the transcription factor (TF) SpiC with these cells. Single-cell RNA sequencing (scRNA-Seq) showed that the macrophages in the adult thymus are composed of two populations distinguished by the expression of Timd4 and Cx3cr1. Remarkably, Timd4⁺ cells were located in the cortex, while Cx3cr1⁺ macrophages were restricted to the medulla and the cortico-medullary junction. Using shield chimeras, transplantation of embryonic thymuses, and genetic fate mapping, we found that the two populations have distinct origins. Timd4⁺ thymic macrophages are of embryonic origin, while Cx3cr1⁺ macrophages are derived from adult hematopoietic stem cells. Aging has a profound effect on the macrophages in the thymus. Timd4⁺ cells underwent gradual attrition, while Cx3cr1⁺ cells slowly accumulated with age and, in older mice, were the dominant macrophage population in the thymus. Altogether, our work defines the phenotype, origin, and diversity of thymic macrophages.

PDGF-AA promotes cell-to-cell communication in osteocytes through PI3K/Akt signaling pathway

Osteocytes are the main sensitive cells in bone remodeling due to their potent functional cell processes from the mineralized bone matrix to the bone surface and the bone marrow. Neighboring osteocytes communicate with each other by these cell processes to achieve molecular exchange through gap junction channels. Platelet-derived growth factor-AA (PDGF-AA) has been reported to enhance bone tissue remodeling by promoting cell proliferation, migration, and autocrine secretion in osteoid cell linage. However, the effect of PDGF-AA on intercellular communication between osteocytes is still unclear. In the present study, we elucidated that PDGF-AA could enhance the formation of dendritic processes of osteocytes and the gap junctional intercellular communication by promoting the expression of connexin43 (Cx43). This modulation process was mainly dependent on the activation of phosphorylation of Akt protein by phosphatidylinositol 3-kinase (PI3K)/Akt (also known as protein kinase B, PKB) signaling. Inhibition of PI3K/Akt signaling decreased the Cx43 expression induced by PDGF-AA. These results establish a bridge between PDGF-AA and cell-cell communication in osteocytes, which could help us understand the molecular exchange between bone cells and fracture healing.

Hematopoietic stem cells produce intermediate lineage adipocyte progenitors that simultaneously express both myeloid and mesenchymal lineage markers in adipose tissue

Some adipocytes are produced from bone marrow hematopoietic stem cells. In vitro studies previously indicated that these bone marrow-derived adipocytes (BMDAs) were generated from adipose tissue macrophage (ATM) that lose their hematopoietic markers and acquire mesenchymal markers prior to terminal adipogenic differentiation. Here we interrogated whether this hematopoietic-to-mesenchymal transition drives BMDA production In vitro. We generated transgenic mice in which the lysozyme gene promoter (LysM) indelibly labeled ATM with green fluorescent protein (GFP). We discovered that adipose stroma contained a population of LysM-positive myeloid cells that simultaneously expressed hematopoietic/myeloid markers (CD45 and CD11b), and mesenchymal markers (CD29, PDGFRa and Sca-1) typically found on conventional adipocyte progenitors. These cells were capable of adipogenic differentiation In vitro and In vitro, while other stromal populations deficient in PDGFRa and Sca-1 were non-adipogenic. BMDAs and conventional adipocytes expressed common fat cell markers but exhibited little or no expression of hematopoietic and mesenchymal progenitor cell markers. The data indicate that BMDAs are produced from ATM simultaneously expressing hematopoietic and mesenchymal markers rather than via a stepwise hematopoietic-to-mesenchymal transition. Because BMDA production is stimulated by high fat feeding, their production from hematopoietic progenitors may maintain adipocyte production when conventional adipocyte precursors are diminished.

Expression and function of PDGF-C in development and stem cells

Platelet-derived growth factor C (PDGF-C) is a relatively new member of the PDGF family, discovered nearly 20 years after the finding of platelet-derived growth factor A (PDGF-A) and platelet-derived growth factor B (PDGF-B). PDGF-C is generally expressed in most organs and cell types. Studies from the past 20 years have demonstrated critical roles of PDGF-C in numerous biological, physiological and pathological processes, such as development, angiogenesis, tumour growth, tissue remodelling, wound healing, atherosclerosis, fibrosis, stem/progenitor cell regulation and metabolism. Understanding PDGF-C expression and activities thus will be of great importance to various research disciplines. In this review, however, we mainly discuss the expression and functions of PDGF-C and its receptors in development and stem cells.

Sprouty1 regulates gonadal white adipose tissue growth through a PDGFRα/β-Akt pathway

Expansion of visceral white adipose tissue (vWAT) occurs in response to nutrient excess, and is a risk factor for metabolic disease. SPRY1, a feedback inhibitor of receptor tyrosine kinase (RTK) signaling, is expressed in PDGFRa+ adipocyte progenitor cells (APC) in vivo. Global deficiency of Spry1 in mice results in disproportionate postnatal growth of gonadal WAT (gWAT), while iWAT and BAT were similar in size between Spry1KO and WT mice. Spry1 deficiency increased the number of PDGFRa+ stromal vascular fraction (SVF) cells in gWAT and showed increased proliferation and fibrosis. Spry1KO gWAT had increased collagen deposition and elevated expression of markers of inflammation. In vitro, SPRY1 was transiently down regulated during early adipocyte differentiation of SVF cells, with levels increasing at later stages of differentiation. SPRY1 deficiency enhances PDGF-AA and PDGF-BB induced proliferation of SVF cells. Increased proliferation of SVF from Spry1KO gWAT accompanies an increase in AKT activation. PDGF-AA stimulated a transient down regulation of SPRY1 in wild type SVF, whereas PDGF-BB stimulated a sustained down regulation of SPRY1 in wild type SVF. Collectively, our data suggest that SPRY1 is critical for regulating postnatal growth of gWAT by restraining APC proliferation and differentiation in part by regulation of PDGFRa/b-AKT signaling.

Spatially defined single-cell transcriptional profiling characterizes diverse chondrocyte subtypes and nucleus pulposus progenitors in human intervertebral discs

A comprehensive understanding of the cellular heterogeneity and molecular mechanisms underlying the development, homeostasis, and disease of human intervertebral disks (IVDs) remains challenging. Here, the transcriptomic landscape of 108 108 IVD cells was mapped using single-cell RNA sequencing of three main compartments from young and adult healthy IVDs, including the nucleus pulposus (NP), annulus fibrosus, and cartilage endplate (CEP). The chondrocyte subclusters were classified based on their potential regulatory, homeostatic, and effector functions in extracellular matrix (ECM) homeostasis. Notably, in the NP, a PROCR⁺ resident progenitor population showed enriched colony-forming unit-fibroblast (CFU-F) activity and trilineage differentiation capacity. Finally, intercellular crosstalk based on signaling network analysis uncovered that the PDGF and TGF-β cascades are important cues in the NP microenvironment. In conclusion, a single-cell transcriptomic atlas that resolves spatially regulated cellular heterogeneity together with the critical signaling that underlies homeostasis will help to establish new therapeutic strategies for IVD degeneration in the clinic.

Spatially defined single-cell transcriptional profiling characterizes diverse chondrocyte subtypes and nucleus pulposus progenitors in human intervertebral discs

A comprehensive understanding of the cellular heterogeneity and molecular mechanisms underlying the development, homeostasis, and disease of human intervertebral disks (IVDs) remains challenging. Here, the transcriptomic landscape of 108 108 IVD cells was mapped using single-cell RNA sequencing of three main compartments from young and adult healthy IVDs, including the nucleus pulposus (NP), annulus fibrosus, and cartilage endplate (CEP). The chondrocyte subclusters were classified based on their potential regulatory, homeostatic, and effector functions in extracellular matrix (ECM) homeostasis. Notably, in the NP, a PROCR+ resident progenitor population showed enriched colony-forming unit-fibroblast (CFU-F) activity and trilineage differentiation capacity. Finally, intercellular crosstalk based on signaling network analysis uncovered that the PDGF and TGF-β cascades are important cues in the NP microenvironment. In conclusion, a single-cell transcriptomic atlas that resolves spatially regulated cellular heterogeneity together with the critical signaling that underlies homeostasis will help to establish new therapeutic strategies for IVD degeneration in the clinic.

Spatially defined single-cell transcriptional profiling characterizes diverse chondrocyte subtypes and nucleus pulposus progenitors in human intervertebral discs

A comprehensive understanding of the cellular heterogeneity and molecular mechanisms underlying the development, homeostasis, and disease of human intervertebral disks (IVDs) remains challenging. Here, the transcriptomic landscape of 108 108 IVD cells was mapped using single-cell RNA sequencing of three main compartments from young and adult healthy IVDs, including the nucleus pulposus (NP), annulus fibrosus, and cartilage endplate (CEP). The chondrocyte subclusters were classified based on their potential regulatory, homeostatic, and effector functions in extracellular matrix (ECM) homeostasis. Notably, in the NP, a PROCR⁺ resident progenitor population showed enriched colony-forming unit-fibroblast (CFU-F) activity and trilineage differentiation capacity. Finally, intercellular crosstalk based on signaling network analysis uncovered that the PDGF and TGF-β cascades are important cues in the NP microenvironment. In conclusion, a single-cell transcriptomic atlas that resolves spatially regulated cellular heterogeneity together with the critical signaling that underlies homeostasis will help to establish new therapeutic strategies for IVD degeneration in the clinic.

Fibroblasts: Origins, definitions, and functions in health and disease

Fibroblasts are diverse mesenchymal cells that participate in tissue homeostasis and disease by producing complex extracellular matrix and creating signaling niches through biophysical and biochemical cues. Transcriptionally and functionally heterogeneous across and within organs, fibroblasts encode regional positional information and maintain distinct cellular progeny. We summarize their development, lineages, functions, and contributions to fibrosis in four fibroblast-rich organs: skin, lung, skeletal muscle, and heart. We propose that fibroblasts are uniquely poised for tissue repair by easily reentering the cell cycle and exhibiting a reversible plasticity in phenotype and cell fate. These properties, when activated aberrantly, drive fibrotic disorders in humans.

Sublytic C5b-9 triggers glomerular mesangial cell proliferation via enhancing FGF1 and PDGFα gene transcription mediated by GCN5-dependent SOX9 acetylation in rat Thy-1 nephritis

Rat Thy-1 nephritis (Thy-1N) is an animal model of human mesangioproliferative glomerulonephritis (MsPGN), accompanied by glomerular mesangial cell (GMC) proliferation and extracellular matrix (ECM) deposition. Although sublytic C5b-9 formed on GMC membrane could induce cell proliferation, the mechanism is still unclear. In this study, we first demonstrated that the level of SRY related HMG-BOX gene 9 (SOX9), general control nonderepressible 5 (GCN5), fibroblast growth factor 1 (FGF1) and platelet-derived growth factor α (PDGFα) was all elevated both in the renal tissues of Thy-1N rats (in vivo) and in the GMCs (in vitro) with sublytic C5b-9 stimulation. Then, we not only discovered that sublytic C5b-9 caused GMC proliferation through increasing SOX9, GCN5, FGF1 and PDGFα expression, but also proved that SOX9 and GCN5 formed a complex and combined with FGF1 and PDGFα promoters, leading to FGF1 and PDGFα gene transcription. More importantly, GCN5 could mediate SOX9 acetylation at lysine 62 (K62) to enhance SOX9 binding to FGF1 or PDGFα promoter and promote FGF1 or PDGFα synthesis and GMC proliferation. Besides, the experiments in vivo also showed that FGF1 and PDGFα expression, GMC proliferation and urinary protein secretion in Thy-1N rats were greatly reduced by silencing renal SOX9, GCN5, FGF1 or PDGFα gene. Furthermore, the renal tissues of MsPGN patients also exhibited positive expression of these genes mentioned above. Collectively, our findings indicate that GCN5, SOX9 and FGF1/PDGFα can form an axis and play an essential role in sublytic C5b-9-triggered GMC proliferation, which might provide a novel insight into the pathogenesis of Thy-1N and MsPGN.

Diet-induced obesity promotes infection by impairment of the innate antimicrobial defense function of dermal adipocyte progenitors

Infections are a major complication of obesity, but the mechanisms responsible for impaired defense against microbes are not well understood. Here, we found that adipocyte progenitors were lost from the dermis during diet-induced obesity (DIO) in humans and mice. The loss of adipogenic fibroblasts from mice resulted in less antimicrobial peptide production and greatly increased susceptibility to Staphylococcus aureus infection. The decrease in adipocyte progenitors in DIO mice was explained by expression of transforming growth factor-β (TGFβ) by mature adipocytes that then inhibited adipocyte progenitors and the production of cathelicidin in vitro. Administration of a TGFβ receptor inhibitor or a peroxisome proliferator-activated receptor-γ agonist reversed this inhibition in both cultured adipocyte progenitors and in mice and subsequently restored the capacity of obese mice to defend against S. aureus skin infection. Together, these results explain how obesity promotes dysfunction of the antimicrobial function of reactive dermal adipogenesis and identifies potential therapeutic targets to manage skin infection associated with obesity.

Genome-wide detection of CNV regions and their potential association with growth and fatness traits in Duroc pigs

Background

In the process of pig breeding, the average daily gain (ADG), days to 100 kg (AGE), and backfat thickness (BFT) are directly related to growth rate and fatness. However, the genetic mechanisms involved are not well understood. Copy number variation (CNV), an important source of genetic diversity, can affect a variety of complex traits and diseases and has gradually been thrust into the limelight. In this study, we reported the genome-wide CNVs of Duroc pigs using SNP genotyping data from 6627 animals. We also performed a copy number variation region (CNVR)-based genome-wide association studies (GWAS) for growth and fatness traits in two Duroc populations.

Results

Our study identified 953 nonredundant CNVRs in U.S. and Canadian Duroc pigs, covering 246.89 Mb (~ 10.90%) of the pig autosomal genome. Of these, 802 CNVRs were in U.S. Duroc pigs with 499 CNVRs were in Canadian Duroc pigs, indicating 348 CNVRs were shared by the two populations. Experimentally, 77.8% of nine randomly selected CNVRs were validated through quantitative PCR (qPCR). We also identified 35 CNVRs with significant association with growth and fatness traits using CNVR-based GWAS. Ten of these CNVRs were associated with both ADG and AGE traits in U.S. Duroc pigs. Notably, four CNVRs showed significant associations with ADG, AGE, and BFT, indicating that these CNVRs may play a pleiotropic role in regulating pig growth and fat deposition. In Canadian Duroc pigs, nine CNVRs were significantly associated with both ADG and AGE traits. Further bioinformatic analysis identified a subset of potential candidate genes, including PDGFA, GPER1, PNPLA2 and BSCL2.

Conclusions

The present study provides a necessary supplement to the CNV map of the Duroc genome through large-scale population genotyping. In addition, the CNVR-based GWAS results provide a meaningful way to elucidate the genetic mechanisms underlying complex traits. The identified CNVRs can be used as molecular markers for genetic improvement in the molecular-guided breeding of modern commercial pigs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07654-7.

Functional regeneration and repair of tendons using biomimetic scaffolds loaded with recombinant periostin

Tendon injuries disrupt the balance between stability and mobility, causing compromised functions and disabilities. The regeneration of mature, functional tendons remains a clinical challenge. Here, we perform transcriptional profiling of tendon developmental processes to show that the extracellular matrix-associated protein periostin (Postn) contributes to the maintenance of tendon stem/progenitor cell (TSPC) functions and promotes tendon regeneration. We show that recombinant periostin (rPOSTN) promotes the proliferation and stemness of TSPCs, and maintains the tenogenic potentials of TSPCs in vitro. We also find that rPOSTN protects TSPCs against functional impairment during long-term passage in vitro. For in vivo tendon formation, we construct a biomimetic parallel-aligned collagen scaffold to facilitate TSPC tenogenesis. Using a rat full-cut Achilles tendon defect model, we demonstrate that scaffolds loaded with rPOSTN promote endogenous TSPC recruitment, tendon regeneration and repair with native-like hierarchically organized collagen fibers. Moreover, newly regenerated tendons show recovery of mechanical properties and locomotion functions.

The regeneration of functional tendons remains a clinical challenge. Here the authors develop a biomimetic scaffold loaded with recombinant periostin and demonstrate its functionality in promoting tendon stem/progenitor cell recruitment and tenogenic differentiation, and tendon regeneration in a rat full-cut Achilles tendon defect model.

Dermal Drivers of Injury-Induced Inflammation: Contribution of Adipocytes and Fibroblasts

Irregular inflammatory responses are a major contributor to tissue dysfunction and inefficient repair. Skin has proven to be a powerful model to study mechanisms that regulate inflammation. In particular, skin wound healing is dependent on a rapid, robust immune response and subsequent dampening of inflammatory signaling. While injury-induced inflammation has historically been attributed to keratinocytes and immune cells, a vast body of evidence supports the ability of non-immune cells to coordinate inflammation in numerous tissues and diseases. In this review, we concentrate on the active participation of tissue-resident adipocytes and fibroblasts in pro-inflammatory signaling after injury, and how altered cellular communication from these cells can contribute to irregular inflammation associated with aberrant wound healing. Furthering our understanding of how tissue-resident mesenchymal cells contribute to inflammation will likely reveal new targets that can be manipulated to regulate inflammation and repair.

Facial Fat Fitness: A New Paradigm to Understand Facial Aging and Aesthetics

Traditionally, facial adipose tissue has been perceived and treated as a homogenous volume-occupying subcutaneous depot. However, recent research from across disciplines is converging to reveal a far more anatomically organized and functionally dynamic role of facial adipose tissue. In this narrative review, we will discuss new insights into adipocyte function and facial adipose anatomy that have far-reaching implications for the practice of aesthetic facial plastic surgery. These concepts are synthesized into a "facial fat fitness" model which can be used to explain clinical observations in facial aging and aesthetic surgery. Fat fitness relates to the quality of facial adipose tissue, as opposed to quantity, and describes whether adipose tissue is in a predominantly healthy hyperplastic or unhealthy hypertrophic state. Fat fitness is modulated by lifestyle factors, and may be impacted positively or negatively by facial aesthetic treatments. LEVEL OF EVIDENCE IV: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Relationships Between Perivascular Adipose Tissue and Abdominal Aortic Aneurysms

Abdominal aortic aneurysms (AAAs) are typically asymptomatic, and there is a high mortality rate associated with aneurysm rupture. AAA pathogenesis involves extracellular matrix degradation, vascular smooth muscle cell phenotype switching, inflammation, and oxidative stress. There is increasing evidence of excessive adipocyte accumulation in ruptured AAA walls. These excessive numbers of adipocytes in the vascular wall have been closely linked with AAA progression. Perivascular adipose tissue (PVAT), a unique type of adipose tissue, can be involved in adipocyte accumulation in the AAA wall. PVAT produces various chemokines and adipocytokines around vessels to maintain vascular homeostasis through paracrine and autocrine mechanisms in normal physiological conditions. Nevertheless, PVAT loses its normal function and promotes the progression of vascular diseases in pathological conditions. There is evidence of significantly reduced AAA diameter in vessel walls of removed PVAT. There is a need to highlight the critical roles of cytokines, cells, and microRNA derived from PVAT in the regulation of AAA development. PVAT may constitute an important therapeutic target for the prevention and treatment of AAAs. In this review, we discuss the relationship between PVAT and AAA development; we also highlight the potential for PVAT-derived factors to serve as a therapeutic target in the treatment of AAAs.